A known damping valve for shock absorber is applied, for example, to a piston unit or the like of a shock absorber for vehicle, is provided with a piston which partitions one chamber and another chamber in the shock absorber, a port which is formed in this piston to allow communication between the one and the other chambers and a leaf valve which is seated on a valve seat surrounding the outer periphery of a window communicating with an output end of this port, and opens the port by deflecting an outer peripheral side of this leaf valve.
In a shock absorber for vehicle, in order to improve the ride quality of a vehicle, it is preferable to firmly damp the vibration of the vehicle by increasing a damping force in a region where a piston speed is low and prevent an excessive damping force by decreasing a damping coefficient when the piston speed reaches a certain high speed. To realize such a damping characteristic (change in damping force in relation to piston speed), various proposals have been made.
For example, in a damping valve for shock absorber disclosed in JP2008-138696A, a piston is divided into a one-side disk and an other-side disk provided to be placed on the one-side disk and formed with a one-side port for permitting the passage of working fluid when a shock absorber extends and an other-side port for permitting the passage of the working fluid when the shock absorber contracts.
Each of the one-side and other-side disks includes an annular inner peripheral seat surface at a corresponding position of each mating surface and an annular outer peripheral seat surface formed at an outer side of the inner peripheral seat surface, and an annular projection is formed on the outer peripheral seat surface of the other-side disk. By squeezing the projection with a nut tightening force, the outer peripheral seat surface of the one-side disk and that of the other-side disk are brought into close contact, thereby preventing the leakage of the working fluid in the middle of the one-side port.
Further, a structure is disclosed in JP1996-261268A which prevents the leakage of working fluid in the middle of a port formed in a divided piston by bringing outer peripheral seat surfaces into close contact via a seal.